1. Field of the Invention
The present invention relates to an ignition coil for an internal combustion engine (hereinafter, referred to as an ignition coil for short).
2. Description of the Prior Art
A structure of an ignition coil for a motor vehicle is, for example, as described in Japanese Unexamined Patent Publication No. 11-111545, constituted by a primary coil wound around a primary spool, a secondary coil wound around a secondary spool which are concentrically arranged in an outer peripheral side of a rod-like center core, a resin member (a potting member or a cast resin) charged into a gap between these plurality of parts, and the like.
However, since coefficients of linear expansion of the respective constituting parts are different from each other, a crack or the like may be generated between the constituting parts (particularly, in a root side of a collar portion in a spool around which a coil winding is arranged) due to a thermal stress. Further, each of the spools is frequently integrally formed by a resin, however, a flow of mold resin is deteriorated in some shapes thereof, so that a void or the like may be generated. Then, since the generation of the crack, the void or the like causes a dielectric breakdown by each of the spools, it is necessary to restrict and prevent them.
The present invention has been achieved by taking the conventional problems mentioned above, and an object of the present invention is to provide an ignition coil for an internal combustion engine which can prevent a crack, a void or the like from being generated, and can secure an insulating property between a primary side and a secondary side.
In order to achieve the object mentioned above, in accordance with the present invention, there is provided an ignition coil for an internal combustion engine comprising:
a resin spool 121 formed in a substantially cylindrical shape;
a coil 120 constituted by a coil winding wound around the spool 121; and
a high electric voltage being supplied to an ignition apparatus in the internal combustion engine,
wherein a plurality of projection portions 121b protruding to an outer side in a diametrical direction from an outer peripheral surface of the spool 121 are integrally formed in an end portion in an axial direction on the outer peripheral surface of the spool 121 so as to line up in a circumferential direction, and a size L of a portion in the projection portion 121b which is in parallel to an axial direction of the spool 121 is larger than a size T of a portion in the projection portion 121b which is in parallel to a direction orthogonal to the axial direction of the spool 121.
Accordingly, in comparison with the spool in accordance with a prior art mentioned below, a resin flow is hard to get out of order near a portion corresponding to the projection portion 121b at a time of forming, and a convoluted void and weld are hard to be generated.
Therefore, in accordance with the present invention, since it is possible to prevent a mechanical strength in a root portion of the projection portion 121b from being reduced, it is possible to previously prevent the crack from being generated in the root side of the projection portion 121b. 
In accordance with the present invention, there is provided an ignition coil for an internal combustion engine comprising:
a resin spool 121 formed in a substantially cylindrical shape;
a coil 120 constituted by a coil winding wound around the spool 121; and
a high electric voltage being supplied to an ignition apparatus in the internal combustion engine,
wherein a projection portion 121b protruding to an outer side in a diametrical direction from an outer peripheral surface of the spool 121 and assembled in the spool 121 after being separately formed from the spool 121 is provided in an end portion in an axial direction on the outer peripheral surface of the spool 121.
Accordingly, since it is possible to make a shape of the spool 121 simple, a resin flow is hard to get out of order at a time of forming the spool 121. Therefore, it is possible to prevent the crack from being generated in the spool 121.
In accordance with the present invention, there is provided an ignition coil for an internal combustion engine comprising:
a resin spool 121 formed in a substantially cylindrical shape;
a coil 120 constituted by a coil winding wound around the spool 121;
a high electric voltage being supplied to an ignition apparatus in the internal combustion engine; and
a resin material having an electric insulating property being charged into a substantially cylindrical housing 172 receiving the coil 120 and the spool 121, whereby the coil 120 and the spool 121 are molded and fixed,
wherein at least a portion corresponding to the coil 120 in the spool 121 has an inner tube portion 121xcex1 and an outer tube portion 121xcex2 so as to form a double cylinder structure, a projection portion 121b protruding to an outer side in a diametrical direction is formed in an end portion in an axial direction of the outer tube portion 121xcex2, and an adhesive strength between the resin material and the outer tube portion 121xcex2 is smaller than an adhesive strength between the resin material and the inner tube portion 121xcex1.
Accordingly, since all of the coil windings in the coil 120 become in a state of being wound on the outer tube portion 121xcex2, a starting point of the crack is hard to be generated in the portion in which the coil winding of the coil 120 is wound. Therefore, it is possible to prevent the crack from being generated and made progress in the portion close to the coil 120.
In accordance with the present invention, there is provided an ignition coil for an internal combustion engine comprising:
a resin spool 121 formed in a substantially cylindrical shape;
a coil 120 constituted by a coil winding wound around the spool 121;
a high electric voltage being supplied to an ignition apparatus in the internal combustion engine; and
a resin material having an electric insulating property being charged into a substantially cylindrical housing 172 receiving the coil 120 and the spool 121, whereby the coil 120 and the spool 121 are molded and fixed,
wherein an adhesion restraining film 122 which restrains an adhesion between an outer peripheral surface of the spool 121 and the coil winding by the resin material is provided between the outer peripheral surface of the spool 121 and the coil winding, and a distance r2 from the adhesion restraining film 122 in an end portion side in an axial direction of the spool 121 to a center axis of the spool 121 is larger than a distance r1 from the adhesion restraining film 122 in a substantially center portion in the axial direction of the spool 121 to the center axis of the spool 121.
Accordingly, since a way (time) until the crack gets to a center portion becomes long, it is possible to prevent the spool 121 from being early broken.
In accordance with the present invention, there is provided an ignition coil for an internal combustion engine comprising:
a primary coil 120 and a secondary coil 120 which are coaxially arranged;
a center core inserted to axial core portions in both of the coils 120 and 130;
an outer peripheral core 140 arranged in an outer peripheral side of both of the coils 120 and 130;
a substantially cylindrical housing 172 receiving both of the coils 120 and 130 and both of the cores 110 and 140; and
a resin material having an electric insulating property being charged into the housing 172, whereby both of the coils 120 and 130 and both of the cores 110 and 140 are molded and fixed,
wherein a slit 141 dividing a part of the outer peripheral coil 140 and extending in a longitudinal direction is provided in the outer peripheral core 140.
Accordingly, since a rigidity of the outer peripheral core 140 is reduced and the outer peripheral core 140 is deformed at a time when a thermal stress is applied, whereby it is possible to absorb the thermal stress, it is possible to prevent the crack from being generated in the spool 121.
In accordance with the present invention, there is provided an ignition coil for an internal combustion engine comprising:
an integrally formed resin spool 121 and a coil 120 constituted by a coil winding wound around the spool 121; and
a high electric voltage being supplied to an ignition apparatus in the internal combustion engine,
wherein the spool 121 is provided with a cylinder portion 121d around which the coil 120 is wound, a collar portion 121b protruding to an outer side in a diametrical direction from an end side outer peripheral surface of the outer portion 121d so as to form a circumferential shape, and a reinforcing portion 121c connected to the collar portion 121b, extending in an axial direction of the cylinder portion 121d and reinforcing the collar portion 121b, and
wherein a ratio of thickness t/t0 of a thickness t of the collar portion 121b and/or the reinforcing portion 121c with respect to a thickness t0 of the cylinder portion 121d is equal to or less than 1.5.
Further, the inventors of the present application have invented a spool shape in which the void or the like is not generated by setting the ratio of thickness t/t0 mentioned above to a predetermined range, even in the case that the collar portion 121b protruding from an end side of the cylinder portion is provided. Further, in this case, since the collar portion 121b and the reinforcing portion 121c are integrally formed, the structure is excellent in view of strength, and it is possible to restrain and prevent generation of the crack or the like.
It is more preferable that this ratio of thickness t/t0 is equal to or less than 1.2, and further equal to or less than 1. In particular, the smaller the thickness of the collar portion and/or the reinforcing portion is, the harder the void or the like is generated.
As a matter of fact, it is preferable that the ratio of thickness t/t0 mentioned above is equal to or more than 0.1, taking a strength, a formability and the like into consideration.
Further, various kinds of shapes can be considered for a shape between the collar portion 121b and the reinforcing portion 121c, however, it is possible to structure, for example, in a manner described in claim 8 or 9.
That is, the reinforcing portion 121c may be extended from a substantially center of the collar portion 121b and form a substantially T shape with the collar portion 121b, or may be extended from both end sides of the collar portion 121b and form a substantially U shape with the collar portion 121b. 
In accordance with the present invention, there is provided an ignition coil for an internal combustion engine comprising:
a coil 120 around which a coil winding is wound;
a resin spool 121 having a cylinder portion 121d around which the coil winding of the coil 120 is wound, and a collar portion 121b protruding to an outer side in a diametrical direction from an outer peripheral surface of the cylinder portion 121d so as to form a circumferential shape and being capable of holding an end portion of the coil 120; and
a high electric voltage being supplied to an ignition apparatus in the internal combustion engine,
wherein an elastic member 123 is provided at least in the coil winding side of the coil 120 connected to the collar portion 121b from the cylinder portion 121d. 
A thermal stress or the like can be applied to the cylinder portion 121d and the collar portion 121b which the coil 120 is in contact with and exists in, due to a difference of coefficients of linear expansion among the respective members. In particular, the thermal stress or the like is easily concentrated to the root portion of the collar portion 121b corresponding to the connecting portion thereof. In accordance with the present invention, since the elastic member 123 reducing the thermal stress or the like is provided therebetween, it is possible to restrain and prevent the generation of the crack or the like in the spool 121 accompanying with the thermal stress or the like.
The elastic member 123 may be, for example, constituted by an elastic film coated on the spool 121. The elastic film can be formed by spraying or painting an elastic resin (for example, an urethane resin), a rubber or the like to the spool 121, or dipping the spool 121 into them.
Further, the elastic member 123 may be constituted by an elastic film which is integrally formed with the spool 121.
In this case, for example, it is possible to integrally form both of the spool 121 and the elastic resin, the rubber or the like by setting the spool 121 to a core and charging the elastic resin, the rubber or the like into a cavity generated in an outer periphery thereof. Further, the elastic film may be formed by winding an elastic film having a heat shrinkability around the spool 121 and thereafter heating this, thereby closely attaching the elastic film to the outer surface of the spool 121.
In accordance with the present invention, there is provided an ignition coil for an internal combustion engine comprising:
a coil 120 in which a coil winding is wound around a substantially cylindrical spool 121; and
a high electric voltage being supplied to an ignition apparatus in the internal combustion engine,
wherein the spool 121 has a cylinder portion 121d, and a collar portion 121b capable of holding an end portion of the coil 120 formed so as to protrude in an outer side in a diametrical direction from an outer peripheral surface of the cylinder portion 121d so as to form a circumferential shape by winding an elastic sheet 123 having linearly arranged projections 123a around the cylinder portion 121d. 
In this case, the collar portion 121b capable of holding the end portion of the coil 120 is not integrally provided with the spool 121, but is formed by winding the elastic sheet 123. Since the elastic sheet 123 is interposed between the coil 120 and the spool 121, the thermal stress or the like applied to a portion between the cylinder portion 121d and the collar portion 121b is reduced, and the crack or the like generated in the root portion or the like of the collar portion 121b can be restrained and prevented.
Further, in the case of integrally forming the spool 121 by the resin, since it is not necessary to integrally form the collar portion 121b by the resin, a resin flow at a time of forming is improved, and it is possible to restrain the generation of void or the like. Further, since the collar portion 121b is formed by winding the elastic sheet 123 corresponding to a separate member from the spool 121, a freedom of design can be increased without being affected by a limitation caused by the generation of the void or the like.
In accordance with the present invention, there is provided an ignition coil for an internal combustion engine comprising:
a coil 120 in which a coil winding is wound around a substantially cylindrical spool 121; and
a high electric voltage being supplied to an ignition apparatus in the internal combustion engine,
wherein the spool 121 is constructed by inserting and fitting an outer tube portion 121xcex2 constituted by an elastic member to an inner tube portion 121xcex1, the outer tube portion 121xcex2 has a cylinder portion 121d around which a coil winding of the coil 120 is wound, and a collar portion 121b protruding to an outer side in a diametrical direction from an outer peripheral surface of the cylinder portion 121d so as to form a circumferential shape and capable of holding an end portion of the coil 120.
Since the spool 121 is constructed by a double structure constituted by the inner tube portion 121xcex1 and the outer tube portion 121xcex2, it is possible to easily form the spool 121 having no void or the like. Further, since the outer tube portion 121xcex2 is constituted by the elastic member, the thermal stress or the like is reduced from the cylinder portion 121d toward the collar portion 121b, and it is possible to restrain and prevent the generation of the crack or the like on the basis thereof.
In accordance with the present invention, there is provided an ignition coil for an internal combustion engine comprising:
a spool formed in a substantially cylindrical shape and having a projection portion 121b arranged in one end portion in an axial direction of an outer peripheral surface;
a coil 120 annularly provided in the spool 121 and having one end constituted by a coil winding held by the projection portion 121b; 
an adhesion restraining film 122 interposed between the spool 121 and the coil winding and restraining an adhesion between the outer peripheral surface of the spool 121 and the coil winding; and
a high electric voltage being supplied to an ignition apparatus in the internal combustion engine,
wherein the ignition coil further has a post-provided collar portion 121f which is annularly provided in the adhesion restraining film 122 at another end portion in an axial direction of the outer peripheral surface of the spool 121 and holding another end of the coil 120.
In conventional, the projection portion 121b and the flange portion 121e are integrally formed at both end portions in the axial direction of the spool 121. Further, the adhesion restraining film 122 is annularly provided in the outer peripheral surface of the spool 121 between the projection portion 121b and the flange portion 121e. Further, the thermal stress applied to the diametrical direction of the ignition coil is shut off by the adhesion restraining film 122.
However, the adhesion restraining film 122 can be annularly provided only between the projection portion 121b and the flange portion 121e. In other words, since the flange portion 121e gets in the way, it is impossible to extend the adhesion restraining film 122 close to the end side in the axial direction over the flange portion 121e of the spool 121.
In this view, in accordance with the present invention, the post-provided collar portion 121f is arranged in place of the flange portion 121e. The post-provided collar portion 121f is annularly provided in the outer peripheral surface of the adhesion restraining film 122 after annularly attaching the adhesion restraining film 122 to the spool 121. Therefore, in accordance with the invention described in claim 15, it is possible to extend the adhesion restraining film 122 close to the end side in the axial direction over the post-provided collar portion 121f. Accordingly, a range in which the thermal stress can be shut off becomes wide, and it is possible to restrain and prevent the generation of the crack or the like.
In accordance with the present invention, there is provided an ignition coil for an internal combustion engine comprising:
a spool 121 formed in a substantially cylindrical shape and having a projection portion 121b arranged in one end portion in an axial direction of an outer peripheral surface;
a coil 120 annularly provided in the spool 121 and having one end constituted by a coil winding held by the projection portion 121b; 
an adhesion restraining film 122 interposed between the spool 121 and the coil winding and restraining an adhesion between the outer peripheral surface of the spool 121 and the coil winding; and
a high electric voltage being supplied to an ignition apparatus in the internal combustion engine,
wherein the coil winding is a self welding coil winding, and the coil 120 is a shape keeping coil 120a capable of keeping a shape by itself.
The shape keeping coil 120a is formed by the self welding coil winding. Accordingly, it is possible to keep the cylindrical shape by itself without holding both ends by the projection portion 121b and the flange portion 121e. Therefore, the flange portion 121e is not required.
In accordance with the present invention, since the flange portion 121e is not arranged, it is possible to extend the adhesion restraining film 122 to the end side in the axial direction. Accordingly, the range in which the thermal stress can be shut off becomes wide, and it is possible to restrain and prevent the generation of the crack or the like.
Here, in the case that the elastic film is provided in the collar portion 121b or the collar portion 121b itself is constituted by the elastic member as in the present invention, the shape of the collar portion 121b provides no problem. Accordingly, the collar portion 121b may be formed in a continuous ring shape, or may be formed in a discontinuous projection shape. As a matter of fact, taking into consideration a flow property of an epoxy resin or the like corresponding to a filler in the inner portion of the housing or the inner portion of the coil, it is preferable that the collar portion 121b is formed in the discontinuous projection shape.
Further, the various kinds of elastic members may employ a structure having a rigidity (Young""s modulus) lower than that of the core member (the inner tube portion) of the spool 121. In the case that the spool 121 is made of a thermosetting resin, for example, a rubber, an urethane resin or the like can be used as the elastic member. Further, the elastic member does not necessarily exist in a whole of the spool, but may partly exist in a range which is effective for reducing the stress such as the thermal stress or the like.
In this case, the spool mentioned above may be constituted by a primary spool and a secondary spool. Further, the projection portion 121b and the collar portion 121b correspond only to convenient appellations, and both of them become substantially the same properly. Further, reference numerals in parentheses indicated in claims and means for solving the problem mentioned above are used only for clarifying a corresponding relation to particular examples described in embodiments mentioned below so as to easily understand the present invention, and do not limit the scope of the present invention to the embodiments mentioned below.